She has definitely done some live performances of her solo albums.
I'm not sure that she's been a guest artist without the rest of gogo. I'm sure she must have done some bass work for SOMEBODY, but I haven't heard of it.
gogo produced for Misono. Yuu and Akko have both done guest vocals. I know Yuu has done guest guitar work. Turkey has done some guest drumming.http://z11.invisionfree.com/gogo7188/index.php?showtopic=77